The present invention relates to plasto-elastomeric compositions comprising thermoplastic olefinic resins and EPDM terpolymers as well as to the process for preparing the same.
The plasto-elastomeric compositions and their manufacturing are well-known in the art. Thus the preparation of thermoplastic compositions from 2-olefinic resins and elastomeric EPDM terpolymers was described for example in FR-2,408,632 and U.S. Pat. No. 3,849,773. For obtaining such compositions, in both the abovementioned patents it is suggested to employ a halogenated phenolic resin or a non-halogenated phenolic resin associated with halogendonors as crosslinking agents in order to achieve a satisfactory crosslinking rate.
From U.S. Pat. No. 4,477,631 it is known to combine the non-halogenated phenolic resin with metal oxides or carbonates thereby enhancing the processability when compared with that of both the patents mentioned above.
Further vulcanization techniques of the elastomer contained in the plasto-elastomeric compositions obtained from 2-olefinic plastomers and ethylene-propylene elastomers utilizing thermodynamic crosslinking, are described for example in DE-2.401.149, U.S. Pat. No. 3.322.360 and U.S. Pat. No. 3.884.882. The elastomeric copolymers, however, are here pre-grafted with maleic anhydride so as to crosslink and render them more compatible with the elastomeric materials contained in said compositions.
At last methods for obtaining plast-elastomeric compositions are also known having the elastomeric phase crosslinked by thermodynamic crosslinking and with the aid of crosslinking agents usually employed in the rubber field, such as sulfur, sulfur donors, organic peroxides, quinone derivatives, guanidines, maleimides, azides, sulfenazides, urea, xanthates, thiazoles, imidazoles, sulfenamides, amines, isocyanates, cyanurates and paraquinon dioxime (see UK-2.011.430, U.S. Pat. No. 3.806.558, U.S. Pat. No. 3.037.954, U.S. Pat. No. 3.758.643 and U.S. Pat. No. 3.862.106).
Common to all the compositions obtained by thermodynamic vulcanization are some disadvantages strongly limiting their use and/or the possibility of an easy manufacturing, such as the non homogeneous crosslinking of the rubbery phase because of the poor crosslinking agents dispersion in the whole plastoelastomeric composition at temperatures similar to or higher than the plastomer melting point, as at such temperatures the crosslinking (or curing) of the elastomeric fraction contained in said composition occurs. Other claimed processes foresee too long reaction times and excessively high crosslinking temperatures, which are not practicable in the industry.